LM2665M6X - National Semiconductor

LM2665

LM2665 Switched Capacitor Voltage Converter

Literature Number: SNVS009E

LM2665

Switched Capacitor Voltage Converter

General Description

The LM2665 CMOS charge-pump voltage converter oper-

ates as a voltage doubler for an input voltage in the range of

+2.5V to +5.5V. Two low cost capacitors and a diode

(needed during start-up) are used in this circuit to provide up

to 40 mA of output current. The LM2665 can also work as a

voltage divider to split a voltage in the range of +1.8V to

+11V in half.

The LM2665 operates at 160 kHz oscillator frequency to

reduce output resistance and voltage ripple. With an operat-

ing current of only 650 µA (operating efficiency greater than

90% with most loads) and 1µA typical shutdown current, the

LM2665 provides ideal performance for battery powered

systems. The device is in SOT-23-6 package.

Features

nDoubles or Splits Input Supply Voltage

nSOT23-6 Package

n12ΩTypical Output Impedance

n90% Typical Conversion Efficiency at 40 mA

n1µA Typical Shutdown Current

Applications

nCellular Phones

nPagers

nPDAs

nOperational Amplifier Power Suppliers

nInterface Power Suppliers

nHandheld Instruments

Basic Application Circuits

Voltage Doubler

10004901

Splitting V

in Half

10004902

September 2005

LM2665 Switched Capacitor Voltage Converter

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

V+ to GND Voltage: 5.8V

OUT to GND Voltage: 11.6V

OUT to V+ Voltage: 5.8V

SD (GND − 0.3V) to (V+ +

0.3V)

V+ and OUT Continuous Output Current 50 mA

Output Short-Circuit Duration to GND (Note 2) 1 sec.

Continuous Power

Dissipation (T

= 25˚C)(Note

600 mW

JMax

(Note 3) 150˚C

(Note 3) 210˚C/W

Operating Junction

Temperature Range

−40˚ to 85˚C

Storage Temperature Range −65˚C to +150˚C

Lead Temp. (Soldering, 10 seconds) 300˚C

ESD Rating 2kV

Electrical Characteristics

Limits in standard typeface are for T

= 25˚C, and limits in boldface type apply over the full operating temperature range. Un-

less otherwise specified: V+ = 5V, C

= 3.3 µF. (Note 4)

Symbol

Parameter Condition

Min

(Note 5)

Typ

(Note 6)

Max

(Note 5) Units

V+ Supply Voltage 2.5 5.5 V

Supply Current No Load 650 1250 µA

Shutdown Supply Current 1 µA

Shutdown Pin Input Voltage Shutdown Mode 2.0

(Note 7) V

Normal Operation 0.8

(Note 8)

Output Current 40 mA

Sum of the R

ds(on)

of the four

internal MOSFET switches I

=40mA 3.5 8Ω

OUT

Output Resistance (Note 9) I

=40mA 12 25 Ω

OSC

Oscillator Frequency (Note 10) 80 160 kHz

Switching Frequency (Note 10) 40 80 kHz

EFF

Power Efficiency R

(1.0k) between GND and

OUT 86 93 %

=40mAtoGND 90

OEFF

Voltage Conversion Efficiency No Load 99 99.96 %

Note 1: Absolute maximum ratings indicate limits beyond which damage to the device may occur. Electrical specifications do not apply when operating the device

beyond its rated operating conditions.

Note 2: OUT may be shorted to GND for one second without damage. However, shorting OUT to V+ may damage the device and should be avoided. Also, for

temperatures above 85˚C, OUT must not be shorted to GND or V+, or device may be damaged.

Note 3: The maximum allowable power dissipation is calculated by using PDMax =(T

JMax −T

A)/θJA, where TJMax is the maximum junction temperature, TAis the

ambient temperature, and θJA is the junction-to-ambient thermal resistance of the specified package.

Note 4: In the test circuit, capacitors C1and C2are 3.3 µF, 0.3Ωmaximum ESR capacitors. Capacitors with higher ESR will increase output resistance, reduce

output voltage and efficiency.

Note 5: Min. and Max. limits are guaranteed by design, test, or statistical analysis.

Note 6: Typical numbers are not guaranteed but represent the most likely norm.

Note 7: The minimum input high for the shutdown pin equals 40% of V+.

Note 8: The maximum input low of the shutdown pin equals 20% of V+.

Note 9: Specified output resistance includes internal switch resistance and capacitor ESR. See the details in the application information for positive voltage doubler.

Note 10: The output switches operate at one half of the oscillator frequency, fOSC =2f

SW.

LM2665

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Test Circuit

Typical Performance Characteristics (Circuit of Figure 1, V+ = 5V unless otherwise specified)

Supply Current vs

Supply Voltage

Supply Current vs

Temperature

10004904 10004905

Output Source

Resistance vs Supply

Voltage

Output Source

Resistance vs

Temperature

10004906 10004907

10004903

FIGURE 1. LM2665 Test Circuit

LM2665

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Typical Performance Characteristics (Circuit of Figure 1, V+ = 5V unless otherwise specified)

(Continued)

Output Voltage Drop

vs Load Current Efficiency vs

Load Current

10004908 10004909

Oscillator Frequency vs

Supply Voltage

Oscillator Frequency vs

Temperature

10004910 10004911

Shutdown Supply

Current vs

Temperature

10004912

LM2665

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Connection Diagram

6-Lead SOT (M6)

10004913

Top View With Package Marking

10004922

Actual Size

Ordering Information

Order Number Package Number Package Marking Supplied as

LM2665M6 MF06A SO4A (Note 11) Tape and Reel (1000 units/rail)

LM2665M6X MF06A SO4A (Note 11) Tape and Reel (3000 units/rail)

Note 11: The first letter "S" identifies the part as a switched capacitor converter. The next two numbers are the device number. The fourth letter "A" indicates the

grade. Only one grade is available. Larger quantity reels are available upon request.

Pin Descriptions

Pin Name

Function

Voltage Doubler Voltage Split

1 V+ Power supply positive voltage input. Positive voltage output.

2 GND Power supply ground input Same as doubler

3 CAP− Connect this pin to the negative terminal of the

charge-pump capacitor Same as doubler.

4SD

Shutdown control pin, tie this pin to ground in normal

operation. Same as doubler.

5 OUT Positive voltage output. Power supply positive voltage input

6 CAP+ Connect this pin to the positive terminal of the

charge-pump capacitor. Same as doubler

Circuit Description

The LM2665 contains four large CMOS switches which are

switched in a sequence to double the input supply voltage.

Energy transfer and storage are provided by external capaci-

tors. Figure 2 illustrates the voltage conversion scheme.

When S

and S

are closed, C

charges to the supply

voltage V+. During this time interval, switches S

and S

are

open. In the next time interval, S

and S

are open; at the

same time, S

and S

are closed, the sum of the input

voltage V+ and the voltage across C

gives the 2V+ output

voltage when there is no load. The output voltage drop when

a load is added is determined by the parasitic resistance

ds(on)

of the MOSFET switches and the ESR of the capaci-

tors) and the charge transfer loss between capacitors. De-

tails will be discussed in the following application information

section.

10004914

FIGURE 2. Voltage Doubling Principle

LM2665

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Application Information

POSITIVE VOLTAGE DOUBLER

The main application of the LM2665 is to double the input

voltage. The range of the input supply voltage is 2.5V to

5.5V.

The output characteristics of this circuit can be approximated

by an ideal voltage source in series with a resistance. The

voltage source equals 2V+. The output resistance R

out

is a

function of the ON resistance of the internal MOSFET

switches, the oscillator frequency, the capacitance and ESR

of C

and C

. Since the switching current charging and

discharging C

is approximately twice as the output current,

the effect of the ESR of the pumping capacitor C

will be

multiplied by four in the output resistance. The output ca-

pacitor C

is charging and discharging at a current approxi-

mately equal to the output current, therefore, its ESR only

counts once in the output resistance. A good approximation

of R

out

is:

where R

is the sum of the ON resistance of the internal

MOSFET switches shown in Figure 2.

The peak-to-peak output voltage ripple is determined by the

oscillator frequency, the capacitance and ESR of the output

capacitor C

High capacitance, low ESR capacitors can reduce both the

output resistance and the voltage ripple.

The Schottky diode D

is only needed for start-up. The

internal oscillator circuit uses the OUT pin and the GND pin.

Voltage across OUT and GND must be larger than 1.8V to

insure the operation of the oscillator. During start-up, D

used to charge up the voltage at the OUT pin to start the

oscillator; also, it protects the device from turning-on its own

parasitic diode and potentially latching-up. Therefore, the

Schottky diode D

should have enough current carrying

capability to charge the output capacitor at start-up, as well

as a low forward voltage to prevent the internal parasitic

diode from turning-on. A Schottky diode like 1N5817 can be

used for most applications. If the input voltage ramp is less

than 10V/ms, a smaller Schottky diode like MBR0520LT1

can be used to reduce the circuit size.

SPLIT V+ IN HALF

Another interesting application shown in the Basic Applica-

tion Circuits is using the LM2665 as a precision voltage

divider. . This circuit can be derived from the voltage doubler

by switching the input and output connections. In the voltage

divider, the input voltage applies across the OUT pin and the

GND pin (which are the power rails for the internal oscillator),

therefore no start-up diode is needed. Also, since the off-

voltage across each switch equals V

/2, the input voltage

can be raised to +11V.

SHUTDOWN MODE

A shutdown (SD) pin is available to disable the device and

reduce the quiescent current to 1 µA. In normal operating

mode, the SD pin is connected to ground. The device can be

brought into the shutdown mode by applying to the SD pin a

voltage greater than 40% of the V+ pin voltage.

CAPACITOR SELECTION

As discussed in the Positive Voltage Doubler section, the

output resistance and ripple voltage are dependent on the

capacitance and ESR values of the external capacitors. The

output voltage drop is the load current times the output

resistance, and the power efficiency is

Where I

(V+) is the quiescent power loss of the IC device,

and I

out

is the conversion loss associated with the switch

on-resistance, the two external capacitors and their ESRs.

The selection of capacitors is based on the specifications of

the dropout voltage (which equals I

out

), the output volt-

age ripple, and the converter efficiency. Low ESR capacitors

(Table 1) are recommended to maximize efficiency, reduce

the output voltage drop and voltage ripple.

Low ESR Capacitor Manufacturers

Manufacturer Phone Capacitor Type

Nichicon Corp. (708)-843-7500 PL & PF series, through-hole aluminum electrolytic

AVX Corp. (803)-448-9411 TPS series, surface-mount tantalum

Sprague (207)-324-4140 593D, 594D, 595D series, surface-mount tantalum

Sanyo (619)-661-6835 OS-CON series, through-hole aluminum electrolytic

Murata (800)-831-9172 Ceramic chip capacitors

Taiyo Yuden (800)-348-2496 Ceramic chip capacitors

Tokin (408)-432-8020 Ceramic chip capacitors

Other Applications

PARALLELING DEVICES

Any number of LM2665s can be paralleled to reduce the

output resistance. Each device must have its own pumping

capacitor C

, while only one output capacitor C

out

is needed

as shown in Figure 3. The composite output resistance is:

LM2665

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Other Applications (Continued)

CASCADING DEVICES

Cascading the LM2665s is an easy way to produce a greater

voltage (A two-stage cascade circuit is shown in Figure 4).

The effective output resistance is equal to the weighted sum

of each individual device:

out

= 1.5R

out_1

out_2

Note that, the increasing of the number of cascading stages

is pracitically limited since it significantly reduces the effi-

ciency, increases the output resistance and output voltage

ripple.

10004919

FIGURE 3. Lowering Output Resistance by Paralleling Devices

10004920

FIGURE 4. Increasing Output Voltage by Cascading Devices

LM2665

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Other Applications (Continued)

REGULATING V

OUT

It is possible to regulate the output of the LM2665 by use of

a low dropout regulator (such as LP2980-5.0). The whole

converter is depicted in Figure 5.

A different output voltage is possible by use of LP2980-3.3,

LP2980-3.0, or LP2980-adj.

Note that, the following conditions must be satisfied simulta-

neously for worst case design:

in_min

out_min

drop_max

(LP2980) + I

out_max

out-

_max

(LM2665)

in_max

out_max

drop_min

(LP2980) + I

out_min

out-

_min

(LM2665)

10004921

FIGURE 5. Generate a Regulated +5V from +3V Input Voltage

LM2665

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Physical Dimensions inches (millimeters) unless otherwise noted

6-Lead Small Outline Package (M6)

NS Package Number MF06A

For Order Numbers, refer to the table in the "Ordering Information" section of this document.

National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves

the right at any time without notice to change said circuitry and specifications.

For the most current product information visit us at www.national.com.

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LM2665 Switched Capacitor Voltage Converter

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